Wireless data communications are a critical component of mobile computing and have become increasingly popular due to the continued development of mobile computing technologies and the deployment of massive infrastructures. The various available technologies that comprise the spectrum of wireless data communications often differ in local availability, coverage range and performance. Cellular networks are one type of wireless data network, where wireless service is provided over a geographical area, and this service area is divided into a number of smaller (sometimes overlapping) regions known as cells. Each cell is served by at least one fixed-location transceiver known as a cell site or base station. When joined together, the network provided by these cells can cover a significantly wide area. This enables a large number of user-operated portable transceivers (e.g., mobile phones, tablets, laptops, etc.) to communicate to other nodes in the network via the base stations, even if some of the transceivers are moving through more than one cell during transmission.
However, cellular data traffic through a single cell is limited by the base station's capacity; there is a finite number of calls or data traffic that a base station can handle at once, depending in part on the physical implementation of the base station and the capacity and resources available to the base station. A mobile device may not be able to connect to a cell at times, or may have severely compromised service, because the radio signals from a base station are too attenuated due to distance (e.g., the mobile device is too far from a base station), or because the phone is in a location where radio signals from a base station are compromised by intervening materials, such as building walls, hills or other structures. Service may be degraded under these conditions. For example, voice quality may suffer, data throughput may be reduced, or calls may be dropped by the network.
As a mobile device travels through coverage areas of multiple base stations, the cellular network keeps track of the mobile device, and the base station that is currently serving the mobile device. The intelligence of the network, and of the mobile device itself, allow the mobile device's data communication to be directed from one base station to the next during conversation to avoid outages. Traditionally, as a mobile device travels, the mobile device constantly detects available signals, selects the base station with the strongest signal available to communicate with, and is released by the base station from which the signal has become weaker. This process of transferring an ongoing call or data session between cells is referred to as a “hand off,” or, from the perspective of the receiving cell, as a “hand in.”
In conventional mobile device communication, the target of a hand off request (e.g., a base station) has no prior knowledge of expected traffic load, nor of expected time of hand in, the Quality of Service (QoS) and load requirement due to an incoming hand offs are normally provided as part of the hand off request. As the traffic load from a single mobile computing device is typically a small fraction of the overall traffic carried by the cell, this approach works well for traditional mobile computing devices.
Due to the nature of mobility, it is difficult to predict when and where a hand off may occur prior to the actual event. Furthermore, there would be limited value to attempting such a prediction. However, when a relatively dense and large amount of mobile devices synchronously and simultaneously travel through cells (such as during transit on mass transit systems, for example), the base station serving the area through which a vehicle of the mass transit system travels may experience a sudden, unanticipated surge of traffic load as the vehicle moves into its coverage area. This unusually high traffic load will persist as the vehicle traverses the coverage of the receiving base station, and then just as abruptly transfers to the next receiving base station.
If a base station is already serving a relatively high load (e.g., several Mobile computing devices), the incoming load for the base station (following the hand-in of the mobile relay node) can be very high, and may exceed the total capacity of the base station. The hand-in of the mobile relay node, with its high traffic load, would put the base station into an overload condition. Historically, base stations have limited options to address this overload condition. For example, a base station might reject the hand off of the mobile relay node altogether, which would result in the loss of connection to hundreds of passengers on the train, or the base station may block the hand off of traffic from some portion of these users, or for certain traffic flows, etc. Virtually all of these alternatives would result in severe performance degradation to the train passengers, and potentially to other users being served by that cell.